1. Field of the Invention
The present invention is directed to hydrophilic amphoteric polyacrylates and a method of preparation. More specifically, these polymers have cationic units located relatively close to the polymer backbone to enhance desirable properties of the polymers. The method of preparation involves reactions of continuous sequences of specified active groups in 1,3 mutual positions with mixture of a primary amine and water.
2. Prior Art Statement
Hydrophilic polymer derivatives of acrylic or methacrylic acid cover a broad range of compositions including salts of polyacrylic acid or polymethacrylic acid, polyacrylamide, N-substituted polyacrylamides or polymethacrylamides, poly (acrylhydroxamic acid) and so forth. The polymers of useful properties are usually copolymers of various combinations of monomers including hydrophilic monomers derived from acrylic and/or methacrylic acids. Such monomers are typically combined either with other hydrophilic co-monomers (such as with other acrylates and/or methacrylates, with vinyl pyrrolidone, with vinylsulfonic acid, styrene sulfonic acid etc.) or with hydrophobic co-monomers (such as alkyl acrylates or methacrylates, styrene. methylstyrene, vinylpyrridine, etc.) The number of possible combinations is too large to name them all, but the great many of them are generally well known to those skilled in the art. Because many derivatives of acrylic and methacrylic acids are similar in many respects, the terms "acrylic derivatives" and "acrylic copolymers" and "acrylic", as used herein shall mean both "acrylic" and "methacrylic" unless stated otherwise.
The most known varieties of hydrophilic polyacrylates and polymethacrylates can be found, for instance, in the following publications:
Philip Molyneux: Water-Soluble Synthetic Polymers, Volumes I and II; CRC Press, Inc., Boca Raton, Fla. (1987);
Nikoloas A. Peppas (Ed.): Hydrogels in Medicine and Pharmacy, Volumes I to III; CRC Press, Inc.
Joseph D. Andrade (Ed.): Hydrogels for Medical and Related Applications; American Chemical Society, Washington, DC (1976)
The copolymers have various molecular arrangements. Some of them are random, such as those manufactured by direct copolymerization of the respective co-monomers. Others may be grafted onto various backbones, such as starch or cellulose; they may have block structure, alternating structure, etc. These polymers and copolymers may also be crosslinked either covalently or by physical interactions between pendant functional groups or by both.
Depending on the crosslinking and polymer composition, the hydrophilicity of acrylic polymers can range in very broad limits; if expressed as equilibrium ratio of the imbibed water to polymer, it can range from about 0.01 (such as polyacrylonitrile) to 1000 (such as crosslinked polyacrylic acid) to infinity (such as in water-soluble polyacrylate salts or polyacrylamide).
Hydrophilic polymeric acrylates and methacrylates play many useful roles in areas of medical devices, pharmaceutical formulations and drug delivery, separation methods in the biomedical industry, in diagnostics, in water treatment, in flocculation, in drag reduction, in cosmetic and personal care products, oil and mining industries, agriculture and many other areas.
This broad applicability implies need for very different compositions and polymer properties. For this reason, there is a continuing search for new polymers with new functional groups, new combinations of old functional groups and new arrangements of groups (block copolymers, alternating copolymers, etc.) which can show benefits for various applications.
In addition to copolymers with neutral, anionic and cationic groups there is a need for so-called amphoteric polymers carrying both anionic and cationic groups in the same polymer chain. Such groups are capable of mutual interactions which provide the polymer with certain special properties: pH dependent swelling, pH dependent crosslinking, etc. For instance, polymers of this class form internal salts at certain well defined pH called isoelectric point. In this respect, amphoteric acrylates are analogous to many proteins and other natural polymers.
The presence of both positive and negative charges on the same chain also provides numerous possibilities of useful interactions with other charged polymers, such as proteins.
One limitation of the current amphoteric polyacrylates is that all hitherto cationic units have their cationic group carried by relatively long pendant groups rather far from the polymer backbone. This distance is known to limit the effect of the charge on swelling and other useful properties. The interactions between charged distantly pendant groups have different character and consequences than interactions between groups which are closely adjacent to the polymer backbone.
Acrylate and methacrylate copolymers can be synthesized by various methods. The method used for the polymer manufacture affects not only the manufacturing costs, but also the polymer structure which, in turn, affects the polymer properties.
The most usual method is copolymerization of the respective co-monomers which, in most cases, leads either to random or to alternating copolymers.
Another of the possible routes to hydrophilic acrylates or methacrylates is chemical modification of another acrylate or methacrylate polymer. Hydrolysis, esterification, transamidation, etc. of acrylic and methacrylic esters and amides are well known to those familiar with this field. Very often the structure and properties of copolymers made in this way differ from those of copolymers of the same composition but made by direct copolymerization.
Some of the possible polymer modifications are reactions of polyacrylonitrile (hereinafter "PAN") or polymethacrylonitrile (hereinafter "PMAN"). The terms PAN and PMAN include both pure polyacrylonitrile and polymethylacrylonitrile, as well as copolymers of at least 85 molar % of acrylonitrile and methacrylonitrile with various co-monomers. Both PAN and PMAN are available and relatively inexpensive polymers.
PMAN is a somewhat less polar and more chemically stable polymer than PAN and PMAN also has the highly polar pendant CN groups in mutual 1, 3 positions. It can also be copolymerized with up to 15 molar % of other monomers without losing its properties important for the present invention. The reactions of PAN and PMAN are typically based on hydrolysis of pendant nitrile group which can yield either primarily amide units or primarily acid units, depending on catalysis (amides are prevailing at acidic catalysis and carboxylates at alkaline catalysis).
Such hydrolysis can be carried out in bulk (heterogeneous reaction in which PAN or PMAN is dispersed in a liquid containing water and a catalyst), in solutions of suitable solvents, or in solvent swollen gels of varying physical nature and consistency. Such reactions are described in the literature as typified by the disclosure of U.S. Pat. No. 3,926,930 to T. Ohfuka et al entitled "Hygroscopic Acrylic Synthetic Fibers and Method for Preparing Same" or U.S. Pat. No. 3,200,102 to H. Kleiner entitled "Process for the Production of Hydrolyzed Acrylonitrile Polymers." If reaction conditions are suitably selected, the hydrolytic reaction of CN groups proceeds via so called "zipper mechanism" which yields multiblock copolymers. The advantage of the multiblock copolymers is that they form very strong hydrogels with water content controllable in wide limits; highly swellable gels are useful as emulsifiers, thickening and viscoelastic agents and thixotropic additives; as absorbents of water, etc.
Zipper hydrolysis of PAN is mostly carried out in solutions. The acid catalyzed reaction is typically done in solutions or gels of inorganic acids, as described, for instance, in the following U.S. Pat. Nos. 4,337,327 (Jun. 29, 1982), 4,379,874 (Apr. 12, 1983), 4,420,589 (Dec. 13, 1983) and 3,897,382 (Jul. 29, 1975).
The base-catalyzed solution hydrolysis of PAN is carried out in aqueous rhodanide solutions as described in U.S. Pat. No. 4,107,121 (Aug. 15, 1978) to Stoy, entitled "Ionogenic Hydrophilic Water-Insoluble Gels from Partially Hydrolyzed Acrylonitrile Polymers and Copolymers, and a Method of Manufacturing Same. Other known reactions of nitrile groups can also be applied to PAN of PMAN, such as hydrazinolysis, alcoholysis and so on yielding the respective derivatives of polyacrylic acid
In solutions of PAN or PMAN, these nonhydrolytic reactions are known to yield typically random copolymers rather than the more useful block copolymers. The block copolymers can be produced by reacting PAN in a special, so called aquagel state (AQG). This AQG state and its reactivity are described in recent U.S. Pat. No. 4,943,618 to V. Stoy, J. Lovy and G. Stoy (Jul. 24, 1990) entitled "Method for Preparing Polyacrylonitrile Copolymers by Heterogeneous Reaction of Polyacrylonitrile Aquagel."
Notwithstanding the state of the art as described above, the particular compositions of the present invention are neither taught nor rendered obvious thereby.